This invention relates to an endoscope apparatus whereby the vein image or the like below the mucous membrane within a body cavity or the like can be observed.
Recently, various electronic endoscopes (also called electronic scopes) wherein a solid state imaging device such as a charge coupled device is used as an imaging means, have been suggested.
Such an electronic endoscope has advantages because the resolution is higher than in a fiber scope, it is easy to record and reproduce picture images and picture image processes such as enlargement and comparison of two picture images are easy.
Now, when distinguishing the affected part and normal part from each other by observing the observed part with the above mentioned electronic endoscope, it will be necessary to sense (recognize) a delicate tone difference.
However, when the variation of the tone of the observed part is delicate, in order to detect this delicate difference, a lot of knowledge and experience will be required and further a long time will be required until it is sensed. Even if attention is concentrated during the sensing, it has been difficult to always make a proper determination.
In order to cope with such circumstances, for example, in the publication of a Japanese patent application of a Japanese patent application laid open No. 3033/1981, there is disclosed a technique wherein, by noting that, in a range other than the visible range as, for example, an infrared wavelength range, some variation of the tone will be large, a spectral light having at least one infrared wavelength range is led in time series to illuminate an object to be observed. The reflected light from the observed object is made to form an image on a solid state imaging device. The image is converted to an electric signal and the electric signal is processed in response to the wavelength range so that a picture image in the wavelength range may be displayed by a specific color signal.
Generally, in an electronic endoscope, a solid state imaging device is photosensitive even to an infrared wavelength range and therefore the image information of the infrared wavelength range can be detected. However, when coloring the image, the image information of the infrared wavelength range will be in the way of balancing the colors. Therefore, in order to elevate the fidelity of the colors, usually, the illuminating light of the infrared wavelength range is prevented by an infrared ray cutting filter or the like from being radiated to the observed object or will be prevented by a provided filter from reaching the light receiving surface of the solid state imaging device even if it is radiated.
According to this prior art example, by using the feature that the light in the infrared range is higher in the penetration degree into a living body or the like than in the visible light range, the observation and recording of an image below the mucous membrane such as the part observed in the infrared range which have been difficult with the observation of the observed part in the visible light range are made possible. This enables, for example, the vein running state below the mucous membrane of an organ to be accurately observed and becomes a help in determining the affected part or the like.
However, in the above mentioned prior art example, for example, an image of a thick vein near the mucous membrane surface can be sensed in the observed part but, as the illuminating light is reflected on the mucous membrane surface in this observed part, the resolution of the image below the mucous membrane will not rise and it has been difficult to sense the information over the details below the mucous membrane.